Solvent refining of wax-containing mixtures



July 17, 1951 E. w. CLARKE 2,561,096

SOLVENT REFINING OF WAX-CONTAINING MIXTURES ax smcir HMP WHX HTI'ESI' Qz Quin Filed Oct. 15, 1947 INVENTOR. f/{yar W'larfi'e "44M 5 KM/ Patented July 17, 1951 1 SOLVENT REFINING OF 'WAX-CONTAINING MIXTURES -Edgar W..Clarke,-.Laurel Springs, N. ..I.,.assignor -.to. The- Atlantic Refining. Cmpany,. Philadelphia, .Pa., a corporation of Pennsylvania 3.? Application 0ctober'15, 1947;.SeriaLNo. 779,922

2 Claims.

- v 1, The present inventionrelates'torthe .treatment of-l-oily waxes,'and more particularly'to-Ethe separation of wax-containing mixtures into fractions ofi higher and lower melting; point.

This-linventioneis especially: applicableto 'the deoilingrof hydrocarbon 'waxes: containing not more than 70% of.-:oil, andtothe separation of wax mixtures" of L lowvoil content into fractions of different-melting I point.

-In accordance with the-invention,=. a waxcontainingnmixturer is; separated into fractions of. higher and lower n1elting point by. admixing the v wax-containing? mixture with". :a selective solvent from thepgroup consisting; of nitr0benzene; phenol, and; pyridine. atrfa temperature above the cloud point of'.the admixtura: cooling the-.-ad-mixture to aetemperaturei belowthe cloud point" such that-two immiscible liquidphases arerformedgonephase comprising a-.-major per-- t-ion of the -.higher melting'wax.-irr*the form' of finely divided: particles suspended ina minor portion. of the. solvent, and the second; phasecomprising a major portion of the solvent contaming dissolvedr lower meltingv wax; oil and color -.bodies,-. separatingthe 'phases' from -one' another; and-removing the solvent from eachs The quantity 0f-so1vent-emp1oyed will usually range from 3' to 5b-volumeszper: volume-of wax' containing m-ixtureto lea-treated, although in some casesas little as 1.5: volumes ohsolventmaybe used. The cloudpoint.willzdepend upon the nature of the wax-containing mixture, as well as upon the composition and:volume of solvent used. must be abovethe cloud point,; and may beabbve the miscibility temperature of the admixture. The cooling is preferably carried to a temperature between 1..F. and 5 F. below the cloud' point, inorder that the higher meltingwax mayv crystallize and form a suspension of: finely divided particles in the immiscible liquid phase. This suspension "is characterized as being nonnlterable :due to .the fineness of' the particles; but

at a= temperature just below. the. cloud point; it

vent encountered in operating at. a temperature above :thecloud: point butbelow miscibility temperature; on 't'he other hand.

The process of the present invention. may be applied in; the wrefining, purification; 'or separation. of wax stocks such as: petroleum. slackv wax;

crude. microcrysta-lline wax, paraflinwaxes, petv The temperature of the initial heating.

rolatum wax,.-..m'ontan wax, ceresin, ozokerite, waxes fromthe destructive-"or non-destructive hydrogenation of mineral oil, synthetic hydrocarbon oil, shale oil, coal, and waxes produced synthetically by the catalytic reaction of hydrocarbons, I or -waxesderived. from the modified FischerrTropsch reaction of carbon monoxide and-hydrogen. 1

The .present invention .may be further understood with reference to the accompanying drawing. which. represents--diagrammatically a 2-stage system. suitable. .for carrying out. the" process.

Refer-ringto. the drawing, thezwax stock in a molten condition isdelivered: fromma. storage. vessel! through. valve-controlled pipe 2 to pipe. 3...surro.unded by a heatin 'jacket. 4 through which steameor other medium may becirculated to...maintain the desired. temperature. A. hot solventextract, for examplernitrobenzene containing. lower.:.melting. wax, oil; andpossibly color bodies is simultaneously. Supplied. .to pipe 3 through pipe #5,. the sourceof suchnsolvent extract bein described. in detail. hereinafter. In passing through jacketed pipe-3, the temperature ofvthe 'wax stock and solvent. extract-is adjusted to-a- Value...above..theoloud. po'intot the. admixperature of the admixture at this stage should.

be from 5 F. to 30 F. above the cloud point. The admixture, at a temperature above its cloud point, is thoroughly agitated in its passage through pump 6, and is delivered by such pump to'a coolin coil 1 or other suitable device for decreasing the temperature. Coil 1 is surrounded by jacket 8 through which brine, water, or other coolingmedium may be circulated. In passing through-.coilz'l, the temperature of the-admixture isrreduced tola value below its cloud point, pref-- erably from 1 F. to 5--F.- below the. cloud point.- As-a resultcof .the' cooling; two immiscible liquid phases are formed, ifnot already in existence, the-highermel-ting wax components bein distributed as finely=divided; non-filterable-particles throughoutathephases. This "mixture is passed from coil. lnthroughva1ve-controlled pipe 9 into settling vessel- HJ- provided. with a rotatable stirrer. Ila-which, if desired, may also function as ascraping-:devicesfor loosening waxwhich may-adhere-tothe: walls of thexvessel-l Inx'vessel- Ill, the mixture is permitted to settle and stratify into two layers, the upper layer comprisin for the most part the higher melting wax particles and a minor amount of solvent, for example, 5% to 20% by volume of the upper layer. The lower layer comprises the major portion of the solvent in which is dissolved the lower melting wax, oil and color bodies (if present). A small amount of finely divided higher melting wax particles may also be entrained in the lower layer, due to failure to pass upwardly from the extract solution into the upper layer comprising the higher melting wax particles. The lower layer is then drawn from settling vessel I and is passed through valve-controlled pipe l2 into a fractionating or stripping tower l3 provided with a heating coil M. In tower I3, the solvent is removed from the lower melting wax byv vaporization, the solvent vapors being taken overhead through pipe I5, condensed in condenser IB, and delivered by valve-controlled pipe H to valve-controlled pipe I8 for further use, as will be described. The lower melting wax is drawn from the bottom of tower l3 and passed by valve-controlled pipe I9 into storage vessel 20.

The upper layer contained in setting vessel l0, comprising the major portion of the higher melting wax in the form of finely divided particles suspended in a minor portion of the solvent, is slowly agitated by rotation of stirrer H, and is drawn from vessel I0 through valve-controlled pipe I8, and is commingled therein with solvent from valve-controlled pipe ll, as well as with solvent delivered by valve-controlled pipe 2 I, the source of which will be hereinafter described. The resulting admixture of finely divided higher melting wax and solvent is passed through pipe 22 surrounded by heating jacket 23, and the temperature of the admixture is brought to a value above the cloud point, and if desired, above the miscibility temperature. The heated mixture is then delivered by pump 24, with thorough agitation, to cooling coil 25 surrounded by jacket 26 through which a cooling medium may be circulated. The temperature of the mixture is reduced to a level a few degrees below its cloud point (1 F. to F.), and the mixture is then delivered by valve-controlled pipe 21 to settling vessel 28 provided with stirrer 29. Herein, the immiscible liquid phases are permitted to settle and stratify, and there is produced an upper ping tower 3|, provided with heating coil 32. In tower 3| the solvent is separated from the higher melting wax by distillation, the wax being withdrawn from the bottom of the tower via valvecontrolled pipe 33 and passed to storage vessel 34. The solvent is taken overhead as vapor through pipe 35, condensed in condenser 36, and delivered by valve-controlled pipe 2| to pipe It! for further use as described hereinbefore.

While the invention has been particularly described with respect to the operation of a 2-stage system, it is obvious that it may likewise be carried out in a system of any desired number of stages, depending upon the degree of separation of the wax-containing mixture required. Preference is had for a system containing from 3 to 5 stages in order to obtain the most efiective separation of the higher and lower melting point waxes.

The present invention may be further illustrated by the followin examples, which, however, are not to be construed as limiting the scope thereof.

(1) A dark colored microcystalline wax having a melting point of 171.5 F. and an oil content of 5% by weight (A. S. T. M. Method D721-44), was extracted at 155 F. with nitrobenzene in a 3-stage system operated in the manner described with reference to the system shown in the drawing. The volume ratio of nitrobenzene to wax stock was 1.57 to 1. There Was obtained as the raffinatefrom the 3rd stage, a light yellow wax amounting to 72.3% of the charge having a melting point of 175.8 F. and an oil content of 3.3% by weight. This material had a miscibility temperature of 173 F. and a cloud point of 159 F. The other fraction, i. e., the extract wax from the 1st stage, was dark brown in color, and had a melting point of 154.5 F. and an oil content of 6.7% by weight. The yield was 27.7% of the charge, and the extract wax had a miscibility temperature of 182 F. and a cloud point of 1545 F. i

(2) A slack wax of brown color having a melting point of 113 F. and an oil content of 41.3%

by weight was extracted in accordance with the present invention in a single stage system, using nitrobenzene as the solvent at a temperature of 90 F. Three different ratios of solvent to wax stock were used, and the results obtained are set forth in the following table.

2.15 :1 3.42 l 6.10 :1 Ratio Solvent Wax Raffinate Extract Raffinate Extract Rafiinate Extract Weight per cent yield 37.6 62. 4 31. 7 68. 3 25. 4 74, 6 Melting point, F. 126. 6 93.0 130.2 93. 8 131. 0 102.0 Oil Content, weight per cent 6 62. 5 5.5 57. 9 5.0 53. 7 Color Yellow Brown Yellow Brown Yellow Brown layer comprising a major portion of the higher melting wax in the form of a fine suspension in a minor amount of solvent, the wax being relatively light colored and of much reduced oil content. The lower layer comprises the major portion of the solvent with minor amounts of lower melting wax, oil, and color bodies, if present. The lower layer is withdrawn from vessel 28 and is recycled by means of valve-controlled pipe 5 to pipe 3 for use as explained hereinbefore.

The upper layer contained in vessel 28 is slowly agitated by stirrer 29, and is passed by valvecontrolled pipe 30 to the fractionating or strip- (3) A refined parafiin wax having a melting point of 134 F. and an oil content of 1.1% by weight was extracted in a single stage system using nitrobenzene as the solvent at F., the ratio of solvent to wax stock being 3.44 to 1. There was obtained a rafiinate yield of 57. having a melting point of 140.4 F. and an oil content of 0.5% by weight, and an extract yield of 42.9% having a melting point of 126.8" F. and an oil content of 1.9% by weight.

While it has been proposed heretofore to treat wax mixtures with various solvents or solvent combinations under various conditions, it has been found that the only solvents suitable for use in accordance with the technique of the present invention and which give commercially interesting results are nitrobenzene, phenol, and pyridine.

I claim:

1. The method of separating a wax-containing mixture into fractions of higher and lower melting point, which comprises admixing said waxcontaining mixture with from 3 to volumes of nitrobenzene at a temperature above the cloud point of the admixture, cooling the admixture to a temperature of 1 F. to 5 F. below the cloud point such that two immiscible liquid phases are formed, one phase comprising a major portion of the higher melting wax in the form of finely divided, unfilterable particles suspended in a minor portion of the nitrobenzene, and the second phase comprising a major portion of the nitrobenzene containing dissolved lower melting wax, oil and color bodies, separating the phases from one another, and removing the nitrobenzene from each.

2. The method of separating a wax-containing mixture into fractions of higher and lower melting point, which comprises admixing said waxcontaining mixture with from 3 to 5 volumes of nitrobenzene at a temperature of 5 F. to 30 F. above the cloud point of the admixture, cooling the admixture to a temperature of 1 F. to 5 F. below the cloud point such that two immiscible liquid phases are formed, one phase comprising a major portion of the higher melting wax in the form of finely divided, unfilterable particles suspended in a minor portion of the nitrobenzene, and the second phase comprising a major portion of the nitrobenzene containing dissolved lower melting wax, oil and color bodies, separating the phases from one another, and removing the nitrobenzene from each.

EDGAR W. CLARKE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,017,432 Bahlke -Oct. 15, 1935 2,063,369 Diggs et a1 Dec. 8, 1936 2,126,493 McKittrick et a1. Aug. 9, 1938 2,160,930 Whiteley et a1. June 6, 1939 2,167,970 Bray Aug. 1, 1939 2,168,330 Ferris Aug. 8, 1939 2,191,136 Tijmstra Feb. 20, 1940 2,302,434 Dons et a1. Nov. 17, 1942 

1. THE METHOD OF SEPARATING A WAX-CONTAINING MIXTURE INTO FRACTIONS OF HIGHER AND LOWER MELTING POINT, WHICH COMPRISES ADMIXING SAID WAXCONTAINING MIXTURE WITH FROM 3 TO 5 VOLUMES OF NITROBENZENE AT A TEMPERATURE ABOVE THE CLOUD POINT OF THE ADMIXTURE, COOLING THE ADMIXTURE TO A TEMPERATURE OF 1* F. TO 5* F. BELOW THE CLOUD POINT SUCH THAT TWO IMMISCIBLE LIQUID PHASES ARE FORMED, ONE PHASE COMPRISING A MAJOR PORTION OF THE HIGHER MELTING WAX IN THE FORM OF FINELY DIVIDED, UNFILTERABLE PARTICLES SUSPENDED IN A MINOR PORTION OF THE NITROBENZENE, AND THE SECOND PHASE COMPRISING A MAJOR PORTION OF THE NITROBENZENE CONTAINING DISSOLVED LOWER MELTING WAX, OIL AND COLOR BODIES, SEPARATING THE PHASES FROM ONE ANOTHER, AND REMOVING THE NITROBENZENE FROM EACH. 